Thread Content
Reposted from: China Adhesives Network. In the context of environmental protection, the use of water-based coatings represents an important trend and approach. However, due to the fact that water-based coatings still lag behind solvent-based coatings in terms of gloss, adhesion, water resistance, as well as leveling and wetting properties, solvent-based coatings still account for the majority of the market in industrial coatings and other specialty coatings. However, as awareness of environmental protection and the efficient use of oil resources continues to grow, the shift toward water-based formulations has become an irreversible trend in the coating industry. Solving technical problems is key to achieving this transition in the coating industry. This article focuses on the application of fluorocarbon surfactants in water-based coatings, particularly water-based plastic coatings, in the hope of contributing to the promotion of such coatings. 1 Properties of fluorocarbon surfactants Fluorocarbon surfactants possess three characteristics that ordinary hydrocarbon surfactants do not have: ① Extremely high surface activity. Even at very low concentrations in water, it can effectively reduce the surface tension of water, thereby improving the wetting and penetration properties of water-based systems; moreover, the fluorocarbon chains possess both hydrophobic and oleophobic properties. ②Excellent stability. ③Production costs are high. In water-based coatings, fluorocarbon surfactants can improve the coating’s wettability and leveling properties on the substrate, as well as its waterproofness; they also enhance dirt resistance, anti-adhesion properties, adhesion strength, and gloss. Additionally, they maintain stability at high temperatures (150–200°C). The use of 2-fluorocarbon surfactants in water-based plastic coatings: Fluorocarbon surfactants can play a certain role in various water-based coatings, yet their actual use is limited at present for two reasons: first, fluorocarbon surfactants are relatively expensive, and some lower-quality water-based coatings do not use such products ； Secondly, since the coatings are applied to the surfaces of wood or metal, the difference in surface tension between the coatings and the substrate is not very large; therefore, ordinary hydrocarbon or silicone surfactants are sufficient to solve the problem, and there is no need to use more expensive fluorocarbon surfactants. However, the situation is different for water-based plastic coatings. On the one hand, the mainstream plastic coating products available on the market today are based on solvent-based acrylic systems, and their high prices have created room for the development of water-based plastic coatings. On the other hand, due to the extremely low surface tension of plastic surfaces, traditional surfactants cannot solve the problem. Therefore, the use of fluorocarbon surfactants in water-based plastic coatings yields the most significant and meaningful results. From a technical perspective, the development of water-based plastic coatings presents three challenges, including: (1) wetting and leveling issues. Plastics are formed by the polymerization of non-polar hydrocarbon-based unsaturated small molecules; they have very low surface tension. It is difficult to wet the surface of plastics using ordinary hydrocarbon or silicone-based surfactants, which leads to issues such as shrinkage or orange peel effect. Moreover, plastic surfaces often contain release agents, which make it difficult for water-based coatings to wet and spread, resulting in the formation of shrinkage cavities. (2) The issue of adhesion force. The most common plastic substrates include PE, PP, ABS, PC, and so on. Judging from the current technological development of water-based resins, adhesion of water-based plastic coatings on ABS and PC is no longer a problem. The use of fluorocarbon surfactants can further enhance adhesion and scratch resistance. For PP and PE, simply adding fluorocarbon surfactants is not sufficient to solve the problem. The solution is often to first treat the surface with an adhesion promoter specifically designed for plastic substrates, and then apply the water-based plastic coating. (3) Problems with aluminum-silver paste. The most common type of plastic coating at present is silver powder paint. For solvent-based coatings, the technology for silver powder paint is well-developed ； For water-based coatings, the price of silver paste and its orientation during the coating drying process are indeed major issues. Domestic water-based aluminum-silver pastes are suitable for use in water-based metal coatings for construction purposes, but they are not suitable for plastic surfaces. The aluminum-silver pastes used on plastic surfaces are still largely monopolized by a few foreign companies. On the other hand, even good aluminum-silver pastes cannot function properly if their orientation is incorrect. Due to the special surface tension effect of fluorocarbon surfactants, they can continue to function during the drying process of water-based coatings, helping to orient the silver paste. In addition to the 3 aspects mentioned above, fluorocarbon surfactants can also help improve the water and solvent resistance of water-based plastic coatings. By reducing the surface friction coefficient of the coating film, its scratch resistance can also be increased. For some water-based plastic coatings that require baking, they can also perform well under high-temperature conditions. Due to the low surface tension of plastics, fluorocarbon surfactants generally need to be added at a solid content of one thousandth in order to function effectively. Precautions for using 3-fluorocarbon surfactants: Taking 3M Fluorad FC-4430 as an example: (1) Addition amount. Fluorocarbon surfactants are relatively expensive; those with a 100% effective content, i.e., pure fluorocarbon surfactants, cost over 1,000 yuan per kilogram in the market. However, the amount of fluorocarbon surfactant added is also very small; compared to 1% for hydrocarbon-based surfactants and 4‰–6‰ for silicone-based surfactants, the amount of fluorocarbon surfactant added is only 0.5‰–1‰. In this case, the cost of the formula increases by around 0.7 to 1.4 yuan; it is slightly higher than when using hydrocarbon-based surfactants or silicone-based surfactants, but it does improve the quality of the product. (2) Usage method. For fluorocarbon surfactants with a 100% solid content, they are generally wax-yellow solids at lower temperatures, and must be heated to melt before use. Before use, it is advisable to prepare a 9.1% solution using polar alcohol ether solvents to facilitate accurate addition. When preparing the dilution solution, only gentle stirring is required to avoid the formation of bubbles. It is best to add it to the system during the paint formulation stage. (3) Environmental protection issues. Speaking of fluoride-related products, some time ago the U.S. Environmental Protection Agency (EPA) issued a statement regarding perfluorooctanoic acid amide (PFOA). Perfluorooctanoic acid amine (PFOA) may pose potential toxicity to humans and the natural environment, and some manufacturers have developed alternative products. In May 2000, the 3M plant voluntarily ceased the production of perfluorooctanoic acid amide. Currently, 3M’s products contain perfluorobutyl fluorocarbon surfactants with a fluorocarbon group of only 4 carbon atoms, and they are manufactured and sold in accordance with the testing standards set by the U.S. Environmental Protection Agency (EPA). (4) Repainting issue. In any formulation system, and under any film-forming conditions, 3MFluoradFC-4430 does not cause issues such as delamination or poor adhesion between the second coating and subsequent coatings. Of course, if different coatings are used for painting, then the issue is a different matter. (5) Compatibility issue. Due to the stability of perfluorocarbon surfactants themselves, especially non-ionic perfluorocarbon surfactants, they hardly react with any strong acids or strong bases. It performs well in various resin systems, including acrylic, polyurethane, amino, and epoxy systems. It also has a synergistic effect on the thickeners, dispersants, and defoamers in the formula. The lower the surface tension of the substrate, the more valuable it is to use fluorocarbon surfactants. Due to the extremely low surface tension of plastics, it is almost essential to use fluorocarbon surfactants in water-based plastic coatings. In terms of the market, there are still few companies in China that produce water-based plastic coatings; the majority are still in the stage of developing formulas for such coatings. However, the prospects for water-based plastic coatings are very promising. It is reported that South Korea’s Samsung has decided to use water-based plastic coatings on all of its mobile phones by the end of 2008, and we believe other phone manufacturers will follow suit. For some export products, due to the stricter environmental standards implemented in Europe and the United States, water-based plastic coatings are being used in an increasing number of such products. Finally, it should be noted that although fluorocarbon surfactants can help solve many problems associated with the use of water-based plastic coatings, they are not a panacea. The properties of the film-forming substances are the most fundamental factors determining the various characteristics of water-based plastic coatings. The widespread use of such coatings depends first and foremost on advancements in resin technology. Proper formulations, production processes, and application methods can all enhance the performance of water-based plastic coatings, while the use of fluorocarbon surfactants can further contribute to their adoption. This post was last edited by hwqckr on 2009-2-16 09:59.]